Merged today was the MR by Sebastian Wick to add an experimental development tool for HDR modes. Right now it amounts to an experimental on/off switch for PQ and Rec2020 formats with displays supporting them. The intention is that in the future this "experimental_hdr" option should also toggle TF, Colorspace, and HDR metadata support too around the high dynamic range desktop support.
This "experimental_hdr" option is only intended right now for testing purposes with HDR displays. More details via this merge request . This experimental option was merged to Mutter Git ahead of the GNOME 44 desktop release later this month.
This comes ahead of Red Hat's HDR/display hackfest taking place next month in the Czech Republic. In particular Red Hat has been a driving force for trying to see GNOME HDR support and for the Linux desktop at large to hopefully finally come together this year with Linux trailing behind Windows and macOS when it comes to high dynamic range support.